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United States Patent |
6,033,592
|
Chandrasekhar
|
March 7, 2000
|
Electrolytes
Abstract
An electrochromic device is provided having an electrochromic conducting
polymer layer in contact with a flexible outer layer. A conductive
reflective layer is disposed between the electrochromic conducting polymer
and a substrate layer. A liquid or solid electrolyte contacts the
conductive reflective layer and a counter electrode in the device. A
liquid electrolyte may comprise, for example, a mixture of sulfuric acid,
poly(vinyl sulfate), and poly(anethosulfonate). A solid electrolyte may
comprise, for example, a mixture of sulfuric acid, poly(vinyl sulfate),
poly(anethosulfonate), and poly(vinyl alcohol). The electrochromic
conducting polymer layer may comprise, for example, poly(diphenyl amine),
poly(4-amino biphenyl), poly(aniline), poly(3-alkyl thiophene),
poly(phenylene), poly(phenylene vinylene), poly(alkylene vinylenes),
poly(amino quinolines), or poly(diphenyl benzidine) and one or more
dopants such as poly(styrene sulfonate), poly(anethosulfonate), poly(vinyl
sulfate), p-toluene sulfonate, trifluoromethane sulfonate, and poly(vinyl
stearate).
Inventors:
|
Chandrasekhar; Prasanna (Freehold, NJ)
|
Assignee:
|
Ashwin-Ushas Corporation (Freehold, NJ)
|
Appl. No.:
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276176 |
Filed:
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March 25, 1999 |
Current U.S. Class: |
252/62.2; 359/270 |
Intern'l Class: |
G02R 001/15 |
Field of Search: |
252/62.6,347,314,307,317
359/270
|
References Cited
U.S. Patent Documents
3807832 | Apr., 1974 | Castellion | 350/160.
|
3844636 | Oct., 1974 | Maricle et al. | 350/160.
|
4215917 | Aug., 1980 | Giglia et al. | 359/272.
|
4272163 | Jun., 1981 | Smokhin et al. | 359/265.
|
4304465 | Dec., 1981 | Diaz | 359/272.
|
4586792 | May., 1986 | Yang et al. | 350/357.
|
4749260 | Jun., 1988 | Yang et al. | 350/357.
|
5079334 | Jan., 1992 | Epstein et al. | 528/210.
|
5124080 | Jun., 1992 | Shabrang et al. | 252/583.
|
5137991 | Aug., 1992 | Epstein et al. | 525/540.
|
5159031 | Oct., 1992 | Epstein et al. | 525/540.
|
5164465 | Nov., 1992 | Epstein et al. | 525/540.
|
5241411 | Aug., 1993 | Arribart et al. | 359/269.
|
5253100 | Oct., 1993 | Yang et al. | 359/266.
|
5413739 | May., 1995 | Coleman | 252/511.
|
5446576 | Aug., 1995 | Lynam et al. | 359/267.
|
5446577 | Aug., 1995 | Bennett et al. | 359/273.
|
5500759 | Mar., 1996 | Coleman | 359/270.
|
5561206 | Oct., 1996 | Yamamoto et al. | 526/256.
|
Other References
P. Chandrasekhar, et al., The International Society for Optical
Engineering, 2528:169-180 (1995).
A. Masulaitis, et al., The Interntional Society for Optical Engineering,
2528:190-197 (1995).
|
Primary Examiner: Koslow; C. Melissa
Attorney, Agent or Firm: Seidel, Gonda, Lavorgna & Monaco, PC
Parent Case Text
This is a divisional of copending application(s) Ser. No. 09/030,170 filed
on Feb. 25, 1998 and which designated the U.S. which is incorporated
herein by reference in its entirety.
Claims
I claim:
1. An aqueous liquid electrolyte comprising
(a) sulfuric acid;
(b) poly(vinyl sulfate); and
(c) poly(anethosulfonate).
2. An aqueous liquid electrolyte according to claim 1, wherein said
sulfuric acid is present in a concentration of from about 0.02 to about
0.4 M, said poly(anethosulfonate) is present in a concentration of from
about 0.002 to about 0.025 M, and said poly(vinyl sulfate) is present in a
concentration of from about 0.02 to about 0.4 M.
3. An aqueous prepared solid electrolyte comprising
(a) sulfuric acid;
(b) poly(vinyl sulfate);
(c) poly(anethosulfonate); and
(d) poly(vinyl alcohol).
4. A solid electrolyte according to claim 3, wherein said
poly(anethosulfonate), poly(vinyl sulfate), sulfuric acid, and poly(vinyl
alcohol) are present in the following molar proportions:
from about 1 to about 200 poly(anethosulfonate);
from about 20 to about 800 poly(vinyl sulfate);
from about 100 to about 800 sulfuric acid; and
from about 2000 to about 10000 poly(vinyl alcohol).
5. An aqueous composition for preparation of a solid electrolyte
comprising:
(a) sulfuric acid in a concentration of from about 0.05 to about 0.4 M;
(b) poly(anethosulfonate) in a concentration of from about 0.0005 to about
0.1 M;
(c) poly(vinyl sulfate) in a concentration of from about 0.01 to about 0.4
M; and
(d) poly(vinyl alcohol) in a concentration of from about 1 M to about 5 M.
6. A nonaqueous solution for preparation of a solid electrolyte comprising:
(a) poly(ethylene oxide) in a concentration of from about 0.05 to about 1.0
M;
(b) poly(ethylene glycol) in a concentration of from about 0.01 to about
0.1 M;
(c) p-toluene sulfonate in a concentration of from about 0.001 to about
0.05 M;
(d) trifluoromethane sulfonate in a concentration of from about 0.01 to
about 0.05 M; and
(e) poly(vinyl sulfate) in a concentration of from about 0.001 to about
0.005 M.
7. A nonaqueous solution according to claim 6 comprising acetonitrile.
Description
FIELD OF THE INVENTION
The invention relates to conducting polymer compositions and electrochromic
devices containing the same. More particularly, the invention relates to
conducting polymer compositions and electrochromic devices which are
responsive in a broad spectral region.
BACKGROUND OF THE INVENTION
Electrochromic materials change color upon application of a voltage.
Electrochromic devices are commonly used in windows, rear view automobile
mirrors, and flat panel displays.
The change in color of an electrochromic material is usually due to an
oxidation/reduction ("redox") process within the electrochromic material.
Most electrochromic devices are responsive in the visible light region.
Electrochromic materials active in the visible spectral region include
metal oxides, such as WO.sub.3, MoO.sub.3 and nickel oxides. Metal oxides
typically range in color from highly colored, such as dark blue, to
transparent.
Conducting polymers are a new class of electrochromic materials which have
recently received attention. Oxidation or reduction of a conducting
polymer, which changes its color and conductivity, is usually accompanied
by an inflow or outflow of counterions in the conducting polymer known as
"dopants". Common dopant counterions include ClO.sub.4.sup.- and
BF.sub.4. For example, the conducting polymer poly(pyrrole) is dark blue
and conductive in its oxidized state ("doped state"). In its reduced state
("de-doped state"), poly(pyrrole) is pale green and non-conductive.
Similarly, poly(aniline) is nearly transparent in its reduced state. When
oxidized with dopants, such as Cl.sup.- and SO.sub.4.sup.2-,
poly(aniline) becomes dark green. During doping of a conducting polymer,
the conducting polymer swells due to the absorption of solvated
counterions and solvent.
Few electrochromic materials are capable of modulating infrared light,
i.e., altering the wavelength and intensity of light in the infrared
region. In fact, most electrochromic materials capable of any change in
the infrared region are static electrochromics, i.e., materials which
cannot be switched between different reflective states. Conducting
polymers are known to exhibit electrochromism in the visible and infrared
regions. Current electrochromic devices which modulate light in the
infrared region are radiators rather than modulators.
There are two types of electrochromic devices--transmissive mode devices
and reflective mode devices. In transmissive mode electrochromic devices,
light passes through the device. The incident light is modulated as it
passes through the device. In contrast, reflective mode electrochromic
devices reflect incident light. The incident light traverses the device
before being reflected. As the incident light and reflected light
traverses the device, the light is modulated.
An important characteristic of an electrochromic device is its "dynamic
range". The dynamic range of an electrochromic device is the difference in
percent reflectance between the extreme electrochromic states of the
electrochromic material at a given wavelength. Other important properties
of an electrochromic device are multicolor capability, broad band
response, switching time and cyclability. Cyclability is the number of
times the color of an electrochromic device may be changed before
significant degradation of the working electrode occurs.
There is a need for flexible flat panel displays of variable area for use
as camouflage for military vehicles and personnel. In particular, the
displays need to be capable of multi-spectral and tailorable operation in
the visible through near infrared to long wave infrared regions,
approximately 0.35 to 24 .mu.m. There is a special interest in devices
capable of operating in the long wave infrared region beyond 8 .mu.m. The
displays need to be thin and able to draped over objects of varying shapes
and sizes.
An example of an electrochromic device which incorporates a conducting
polymer is U.S. Pat. No. 5,253,100, issued to Yang ("the Yang patent").
The Yang patent discloses an electrochromic device containing two layers
of poly(aniline) as the electrochromic material. The first layer is
preferably poly(aniline)/poly(styrene sulfonate) (PSS.sup.-) or
poly(aniline)/acrylate obtained by electrochemical polymerization of
poly(aniline) in poly(styrene sulfonate) (PSS) or poly(acrylic acid). The
second (less dense) layer is prepared by chemical polymerization of
aniline monomer in a template of acrylic acid or HPSS to yield a
processible composite which can be coated. The device further contains
solid electrolyte. The solid electrolyte includes typical solid
electrolyte components such as poly(vinyl sulfonate), poly(styrene
sulfonate), poly(acrylic acid, salt) (PAA), poly(-2-acrylamido-2-methyl
propane sulfonic acid) and poly(phosphazenes).
The device of the Yang patent has a sandwich structure which preferably
comprises the following layers in the order recited: glass, indium tin
oxide (ITO), solid electrolyte, second layer of poly(aniline), first layer
of poly(aniline), ITO, and glass. The solid electrolyte is in contact with
the second layer of poly(aniline). The second poly(aniline) layer is said
to aid solid electrolyte penetration and contact with the first
poly(aniline) layer. Yang discloses that the combination of the solid
electrolyte and the two layers of poly(aniline) increases the efficiency
of the device.
The Yang device is inflexible due to the glass outer layers. The glass
outer layer can not be substituted with poly(ethylene), since ITO and all
other transparent conductors cannot be deposited on poly(ethylene) without
cracking. If the first ITO layer were replaced by a thin metal layer, such
as gold, there would be a trade off of thickness versus opacity. The gold
layer at a thickness required for efficient device operation would be
substantially opaque. Furthermore, the layers of glass, ITO, and
electrolyte are opaque to infrared light; the electrochromic material of
the Yang device is not responsive in the infrared region.
Maricle et al., U.S. Pat. No. 3,844,636, discloses a reflective mode
electrochromic mirror utilizing WO.sub.3 as the electrochromic material.
The electrochromic material is sandwiched between a glass front layer and
an ion porous layer. The ion porous layer is composed of a conductive
reflective material. An electrolyte layer is adjacent the ion porous
layer. A counter electrode layer is adjacent the electrolyte layer, such
that the electrolyte layer separates the ion porous layer from the counter
electrode layer. The electrochromic material, WO.sub.3, is infrared opaque
and incapable of infrared modulation. The mirror is inflexible due to the
glass front layer. Flexibility cannot be achieved by substituting plastics
for the glass, since WO.sub.3 is incohesive, cracks, and peels on flexible
substrates.
Castellion, U.S. Pat. No. 3,807,832, discloses a reflective mode
electrochromic mirror. The electrochromic material may be a metal oxide
such as WO.sub.3 or MoO.sub.3. The electrochromic material is sandwiched
between a transparent conductive electrode and a layer of electrolyte. A
porous reflective layer is disposed in the electrolyte. A counter
electrode is in contact with the electrolyte. The electrochromic
materials, metal oxides such as WO.sub.3 and MoO.sub.3, are opaque in the
infrared region and incapable of modulation of light in the infrared
region. The mirror is inflexible since the electrochromic material and the
transparent conductive electrode are composed of materials which are
inflexible.
Bennett et al., U.S. Pat. No. 5,446,577, ("the Bennett et al. patent")
discloses a reflective mode electrochromic display comprising the
following layers in the order recited: first transparent layer,
electrolyte, electrochromic material, metallized electrode, and second
transparent layer. Conducting, polymers, including poly(aniline),
poly(pyrrole), poly(thiophene), poly(phenylene sulfide), and
poly(acetylene), may be employed as the electrochromic material. However,
poly(phenylene sulfide) and poly(acetylene) are electrochromically poor or
inactive. The conducting polymer is paired with a dopant, such as a
sulfate or chloride. In the examples in the Bennett et al. patent, the
electrolyte is an aqueous acidic solution containing poly(acrylic acid).
Liquid propylene carbonate and solid poly(ethylene oxide) are disclosed as
alternative electrolytes.
The Bennett et al. device is unable to modulate light in the infrared
region for several reasons. First, since the electrolyte layer is
contained between the transparent outer layer and the electrochromic
material, an incident beam of light must traverse the electrolyte before
interacting with the electrochromic material. All of the electrolytes
disclosed by Bennett et al. absorb a substantial amount of light in the
infrared region. Therefore, the electrolyte layer seriously impedes
infrared signals reflected by the Bennett et al. device. Second, all the
combinations of conducting polymers and dopants described modulate light
in the infrared region extremely poorly or not at all. Lastly, with the
exception of poly(ethylene), all the transparent layers described are
substantially infrared opaque.
SUMMARY OF THE INVENTION
According to the present invention, a flexible electrochromic device is
provided comprising a flexible outer layer, an electrode, and one or more
counter electrodes. The electrode comprises an electrochromic conducting
polymer layer in contact with the flexible outer layer; and an
electrolyte-permeable substrate layer; and a conductive reflective layer
disposed between the substrate layer and the electrochromic conducting
polymer layer. The electrochromic device further comprises an electrolyte
in contact with the conductive reflective layer and the one or more
counter electrodes.
According to another embodiment of the invention, an aqueous liquid
electrolyte is provided comprising sulfuric acid, poly(vinyl sulfate), and
poly(anethosulfonate).
According to another embodiment of the invention, an aqueous prepared solid
electrolyte is provided comprising sulfuric acid, poly(vinyl sulfate),
poly(anethosulfonate), and poly(vinyl alcohol).
According to another embodiment of the invention, a nonaqueous prepared
solid electrolyte is provided comprising poly(ethylene oxide),
poly(ethylene glycol), poly(anethosulfonate), poly(vinyl sulfate), and one
or more dopants selected from the group consisting of
poly(anethosulfonate), p-toluene sulfonate, trifluoromethane sulfonate,
poly(vinyl stearate), and poly(vinyl sulfate).
According to another embodiment of the invention, a polymeric matrix is
provided comprising one or more conducting polymers selected from the
group consisting of poly(diphenyl amine), poly(4-amino biphenyl),
poly(aniline), poly(3-alkyl thiophene), and poly(diphenyl benzidine) and
one or more dopants selected from the group consisting of
poly(anethosulfonate), p-toluene sulfonate, poly(vinyl sulfate),
trifluoromethane sulfonate, and poly(vinyl stearate). According to a
preferred embodiment, the polymeric matrix comprises poly(aniline),
poly(anethosulfonate), and poly(vinyl sulfate).
According to another embodiment of the invention, an electrochromic device
comprises: an electrode comprising an electrochromic material; one or more
counter electrodes; and an electrolyte in contact with the electrochromic
material and the one or more counter electrodes, which electrolyte
comprises sulfuric acid, poly(vinyl sulfate) and poly(anethosulfonate).
According to another embodiment of the invention, an electrochromic device
is provided comprising: an electrode comprising an electrochromic
material; one or more counter electrodes; and an electrolyte in contact
with the electrochromic material and the one or more counter electrodes,
which electrolyte comprises: poly(ethylene oxide); poly(ethylene glycol);
poly(anethosulfonate); poly(vinyl sulfate); and one or more dopants
selected from the group consisting of poly(anethosulfonate), p-toluene
sulfonate, trifluoromethane sulfonate, poly(vinyl stearate), and
poly(vinyl sulfate).
DESCRIPTION OF THE DRAWINGS
For the purpose of illustrating the invention, there is shown in the
drawings a form which is presently preferred. It being understood,
however, that this invention is not limited to the precise arrangements
and instrumentalities shown.
FIG. 1 is a cross-sectional view of an electrochromic device according to
the present invention.
FIG. 2 is a cross-sectional view of a second embodiment of an
electrochromic device according to the present invention.
FIG. 3A is a partial cross-sectional view of the electrochromic device in
FIG. 1 before "break-in".
FIG. 3B is a partial cross-sectional view of the electrochromic device in
FIG. 1 after "break-in".
FIG. 4 is a specular Fourier Transform Infrared (FTIR) spectrum of the
electrochromic device of Example 1.
FIG. 5 is a diffuse FTIR spectrum of the electrocliromic device of Example
1.
FIG. 6 is a diffuse Ultraviolet-Visible-Near Infrared (UV-Visible-NIR)
spectrum of the electrochromic device of Example 1.
FIG. 7 is a specular FTIR spectrum of the electrochromic device of Example
2.
FIG. 8 is a diffuse FTIR spectrum of the electrochromic device of Example
2.
FIG. 9 is a diffuse UV-Visible-NIR spectrum of the clectrochromic device of
Example 2.
FIG. 10 is a specular FTIR spectrum of the electrochromic device of Example
3.
FIG. 11 is a diffuse FTIR spectrum of the electrochromic device of Example
3.
FIG. 12 is a diffuse UV-Visible-NIR spectrum of the electrochromic device
of Example 3.
FIG. 13 is a cyclic voltammogram of the electrochromic device of Example 4.
FIG. 14 is a specular FTIR spectrum of the electrochromic device of Example
4.
FIG. 15 is a diffuse FTIR spectrum of the electrochromic device of Example
4.
FIG. 16 is a specular UV-Visible-NIR spectrum of the electrochromic device
of Example 4.
FIG. 17 is a specular FTIR spectrum of the electrochromic device of
Comparative Example 5.
FIG. 18 is a diffuse FTIR spectrum of the electrochromic device of
Comparative Example 5.
FIG. 19 is a specular FTIR spectrum of the electrochromic device of
Comparative Example 6.
FIG. 20 is a diffuse FTIR spectrum of the electrochromic device of
Comparative Example 6.
FIG. 21 is a specular FTIR spectrum of the electrochromic device of
Comparative Example 7.
FIG. 22 is a specular FTIR spectrum of the electrochromic device of
Comparative Example 8.
FIG. 23 is a diffuse FTIR spectrum of the electrochromic device of
Comparative Example 8.
FIG. 24 is a diffuse UV-Visible-NIR spectrum of the electrochromic device
of Comparative Example 8.
FIG. 25 is a specular FTIR spectrum of the electrochromic device of
Comparative Example 9.
FIG. 26 is a diffuse FTIR spectrum of the electrochromic device of
Comparative Example 9.
FIG. 27 is a specular UV-Visible-NIR spectrum of the electrochromic device
of Comparative Example 9.
FIG. 28 is a bar graph comparing the diffuse reflectance dynamic ranges at
5 .mu.m of the electrochromic devices of Examples 2, 6, 7, 8 and 9.
FIG. 29 is a specular FTIR spectrum of the electrochromic device of Example
10.
FIG. 30 is a diffuse FTIR spectrum of the electrochromic device of Example
10.
FIG. 31 is a specular FTIR spectrum of the electrochromic device of Example
11.
FIG. 32 is a diffuse FTIR spectrum of the electrochromic device of Example
11.
FIG. 33 is a diffuse UV-Visible-NIR spectrum of the electrochromic device
of Example 11.
FIG. 34 is a specular FTIR spectrum of the electrochromic device of Example
12.
FIG. 35 is a diffuse FTIR spectrum of the electrochromic device of Example
12.
FIG. 36 is a diffuse UV-Visible-NIR spectrum of the electrochromic device
of Example 12.
FIG. 37 is a specular FTIR spectrum of the electrochromic device of Example
13.
DESCRIPTION OF THE INVENTION
Referring to the drawings, wherein like numerals indicate like elements,
there is shown in FIG. 1 an electrochromic device 10 according to the
invention. A substantially transparent outer layer 12 is located at the
viewing side (front) of the device 10. Incident light enters the device 10
through the transparent outer layer 12, which is the front of the device.
The transparent outer layer 12 has a top edge 14 and a bottom edge 16. An
electrochromic conducting polymer layer 18 is in intimate physical contact
with the transparent outer layer 12 along the conducting polymer layer
outer surface 15. The electrochromic conducting polymer layer 18 is in
contact with an electrolyte-permeable substrate layer 20 along the
conducting polymer layer's opposite (i.e., inner) surface. The
electrochromic conducting polymer layer 18 may further comprise a dopant.
The electrolyte-permeable substrate layer 20 contains a solid electrolyte.
Alternatively, the electrolyte-permeable substrate layer 20 may contain a
liquid electrolyte instead of a solid electrolyte. The
electrolyte-permeable substrate layer 20 has a conductive reflective
surface 22. The conductive reflective surface 22 is formed on the surface
of the electrolyte-permeable substrate layer 20 by metallization. The
conductive reflective surface 22 is in contact with the electrochromic
conducting polymer layer 18 and the electrolyte. The electrochromic
conducting polymer layer 18, and the electrolyte-permeable substrate layer
20 with the conductive reflective surface 22 deposited thereon, together
form a working electrode.
A counter electrode film 26 contacts the electrolyte-permeable substrate
layer 20. Preferably, the counter electrode film 26 is formed from a
conducting polymer and comprises the same conducting polymer forming the
electrochromic conducting polymer layer 18. The counter electrode film 26
is in contact with the electrolyte. A second substrate layer 28 is in
contact with the counter electrode film 26. The second substrate layer 28
is comprised of a an electrolyte-permeable or electrolyte-impermeable
flexible material. A conductive surface 30 is metallized onto the surface
of the second substrate layer 28 contacting counter electrode film 26. The
conductive surface 30 is in contact with the counter electrode film 26.
The counter electrode film 26, and the second substrate layer 28 with the
conductive surface 30 deposited thereon, together form a counter
electrode.
Electrical connector 36 attaches to the conductive reflective surface 22 of
the electrolyte-permeable substrate layer 20. Electrical connector 38
attaches to the conductive surface 30 of the second substrate layer 28.
The counter electrode formed by film 26 and second substrate layer 28 may
be positioned behind the working electrode formed by electrochromic
conducting polymer layer 18 and first porous substrate layer 20. This
arrangement is shown in FIG. 1. Alternatively, the device 10 may have two
or more counter electrodes positioned above and/or below the working
electrode as illustrated in FIG. 2.
An encapsulant 34 may surround the electrode/counter electrode assembly,
except for the transparent outer layer 12, to enclose the assembly and
permit handling. The composition of the encapsulant, and its method of
application, is described later. The transparent outer layer 12 may be
comprised of the same material as the encapsulant 34, or may be comprised
of a different material. The transparent outer layer 12 should be as thin
as possible in order to maximize the transmission of the transparent outer
layer 12.
In operation, incident light enters the device 10 through the transparent
outer layer 12. The incident light traverses the thickness of the
electrochromic conducting polymer layer 18 and is reflected by the
conductive reflective surface 22. The reflected light traverses the
electrochromic conducting polymer layer 18 in the opposite direction of
the emitted light and exits the device. The wavelength and intensity of
the incident light is modulated by the electrochromism of the
electrochromic conducting polymer layer 18.
FIG. 2 illustrates an alternative embodiment of the present invention
comprising two counter electrodes. An electrochromic conducting polymer
layer 18' is in intimate physical contact with transparent outer layer 12'
along the conducting polymer outer surface 15'. The electrochromic
conducting polymer layer 18' is in contact with an electrolyte-permeable
substrate layer 20' along the conducting polymer layer's opposite (i.e.,
inner) surface. The conducting polymer of layer 18' may contain a dopant.
The electrolyte-permeable substrate layer 20' contains a solid or liquid
electrolyte. A conducting reflective surface 22' is present on the surface
of layer 20' and in contact with electrochromic conducting polymer layer
18' and electrolyte. The electrochromic conducting polymer 18', and the
electrolyte-permeable substrated layer 20' with conductive reflective
surface 22' deposited thereon, together form a working electrode.
The electrochromic device 10' further contains a first counter electrode 32
and a second counter electrode 50. The two counter electrodes 50 and 32
are positioned at the top and bottom of the working electrode,
respectively. Counter electrode 50 comprises a counter electrode film 52
and a substrate layer 54. A conductive surface 56 is metallized onto the
surface of the substrate layer 54. The conductive surface 56 is in contact
with the counter electrode film 52. Counter electrode 32 comprises a
counter electrode film 26' and a substrate layer 28'. A conductive surface
30' is metallized onto the surface of the substrate layer 28'. The
conductive surface 30' is in contact with the counter electrode film 26'.
Preferably, the second counter electrode 50 is composed of the same
materials as the first counter electrode 32.
A substrate layer 60 is disposed between electrolyte-permeable substrate
layer 20' and encapsulant 34'. Electrical connectors 36', 38' and 62
attach to the electrolyte-permeable substrate layer 22', conductive
surface 30' and conductive surface 56, respectively.
The two counter electrodes 32 and 50 may be rolled (as shown in FIG. 2),
much like a tight cigarette wrapper, such that the counter electrode film
26' and 52 of each counter electrode contacts the porous substrate 20' of
the working electrode. The electrolyte permeates the rolled up counter
electrodes.
The electrolyte-permeable substrate layer 20 provides rigidity to the
electrochromic device and support to the electrochromic conducting polymer
layer 18. The substrate material of layer 20 should be compatible with the
conducting polymer and electrolyte of the device. Also, the substrate
material should be capable of being metallized. The substrate material may
comprise, but is not limited to, any of the following, or combinations
thereof: poly(propylene), poly(ethylene terephthalate), poly(ethylene),
poly(methyl methacrylate), poly(ethyl methacrylate),
poly(tetrafluoroethylene) and other fluorinated poly(alkylenes), nylon,
poly(vinylidene fluoride), acrylics (such as methyl methacrylate synthetic
resins, acrylate synthetic resins, and thermoplastic poly(methyl
methacrylate)-type polymers), acrylonitrile methyl acrylate copolymers,
ethylene vinyl acetate, fluorinated ethylenepropylene resins,
poly(carbonates), poly(butylenes), poly(vinyl chloride), poly(urethanes),
poly(imides), woven or nonwoven porous man-made or natural textile cloths,
and papers (including filter papers). Preferably, the substrate material
is poly(propylene), poly(ethylene terephthalate),
poly(tetrafluoroethylene), poly(ethylene), nylon or poly(vinylidene
fluoride). Most preferably, the substrate material is poly(propylene),
poly(ethylene), poly(ethylene terephthalate), poly(vinylidene flouride) or
nylon.
The electrolyte-permeable substrate layer 20 may take the form of a sheet
or membrane. It may be supported or laminated on an inert flexible support
such as a support comprising poly(propylene) or poly(tetrafluoroethylene).
The electrolyte-permeable substrate layer 20 is formed of a material which
permits passage of electrolyte therethrough. The substrate layers 20 and
28 should have adequate conductivity to conduct a current through the
device. This enables electrical contact between the working electrode
formed by electrochromic conducting polymer layer 18 and
electrolyte-permeable substrate layer 20, and the counter electrode formed
by counter electrode film 26 and second substrate layer 28. Electrical
contact is maintained through the electrolyte contained in the
electrolyte-permeable substrate layer 20.
The electrolyte-permeable substrate layer 20 may comprise any material
which may be penetrated by the electrolyte contained in the electrochromic
device. For example, substrate layer 20 may comprise any flexible porous,
microporous, perforated or microperforated material. Porous and
microporous materials are typically characterized by the presence of pores
which are generated as a consequence of the material manufacturing
process. Materials having pore sizes greater than about 100 .mu.m are
generally known as "porous", while materials having pore sizes of 100
.mu.m or less are generally known as "microporous".
Perforated and microperforated materials comprise solid materials into
which perforations are introduced, typically by mechanical manipulation of
the material following manufacture. Perforations may be made by methods
such as, but not limited to, physical puncturing and etching. Materials
having perforations greater than 100 .mu.m are generally known as
"perforated", while materials having perforations 100 .mu.m or less are
generally known as "microperforated".
Where a microporous substrate is selected as the electrolyte-permeable
substrate layer 20, the pores should be smaller than about 25 .mu.m. At
pore sizes larger than 25 .mu.m, interference with the reflected light in
the electrochromic device may occur because the pores in a microporous
substrate are typically close together. No such restriction is placed on
the perforation size of microperforated substrates, since the perforations
are not close together and therefore do not distort the reflected light.
Preferably, microporous substrates utilized to form substrate layer 20
have a pore size from about 0.05 .mu.m to about 10 .mu.m.
Where a perforated material is used to form substrate layer 20, the
perforations have a size of about 0.2 mm, and the perforations are spaced
about 1.5 mm apart.
The second substrate layer 28 may comprise any of the materials described
for the electrolyte-permeable substrate layer 20, or any flexible natural
or plastic material which may be metallized. The material should be
chemically and physically compatible with the conducting polymer/dopant
and electrolyte.
The conductive reflective surface 22 on the electrolyte-permeable substrate
layer 20, and the conductive surface 30 on the second substrate layer 28,
may be formed by metallization methods which include, but are not limited
to, thermal evaporation, DC magnetron sputtering and electroless plating.
The conductive reflective surface 22 provides electrical contact between
the electrochromic conducting polymer layer 18 and the electrolyte.
Preferably, the conductive reflective surface 22 and the conductive
surface 30 comprise Ir, Pt, Au, Rh, Cu, Ag, or Ni. Most preferably, the
electrolyte-permeable substrate layer 20 and the second substrate layer 28
are metallized with Au due to its superior reflectivity in both the
visible and infrared regions, excellent mechanical properties,
flexibility, chemical inertness and compatibility with conducting
polymer/dopant combinations and electrolytes.
The metal must be deposited on the electrolyte-permeable substrate layer 20
such that the porosity of the substrate is maintained. Also, the
metallized layer 20 must maintain adequate reflectivity. Preferably, the
metal layer is deposited on substrate layers 20 and 28 to a thickness of
from about 50 nm to about 600 nm.
The metal may be deposited on the electrolyte-permeable substrate layer 20
through a mask in the pattern of a grid. The deposited metal may be
continuous, and may be discontinuous such as in the form of a grid. Where
the metallized layer is in the form of a grid, the electrochromic device
may alter the wavelength and intensity of incident light in the microwave
region of the electromagnetic spectrum. By varying the pattern of the grid
and distance between grid lines, different wavelengths of light in the
microwave region may be modulated by the device.
The conducting polymer alters the wavelength and intensity of incident
light reflected by the device. The selection of the conducting polymer or
conducting polymer/dopant combination for the electrochromic conducting
polymer layer 18 is critical to the performance of the electrochromic
device, especially in the infrared region. Performance criteria of the
conducting polymer/dopant combination include high color contrast or
multicolors in the visible region, and large and broad band dynamic range
in the infrared region. Other performance criteria include thermal
stability, environmental stability, mechanical durability and flexibility.
The electrochromic conducting polymer layer 18 may comprise any conducting
polymer satisfying the aforementioned performance criteria. Preferably,
the electrochromic conducting polymer is poly(diphenyl amine),
poly(4-amino biphenyl), poly(aniline), poly(3-alkyl thiophene)
(alkyl=methyl through octyl), poly(diphenyl benzidine), poly(phenylene),
poly(phenylene vinylene), a poly(alkylene vinylene), a poly(amino
quinoline) or derivatives or copolymers thereof. The electrochromic
conducting polymer layer 18 may also comprise combinations of two or more
of the aforementioned conducting polymers.
When poly(aniline) is utilized for layer 18, it is preferably synthesized
in an aqueous environment. More preferably, poly(aniline) is synthesized
in an acidic aqueous environment. Poly(aniline) may also be synthesized by
nonaqueous electropolymerization.
The electrochromic conducting polymers other than poly(aniline) are
preferably synthesized in a nonaqueous environment, most preferably in a
nonaqueous environment acetonitrile medium.
The electrochromic conducting polymer layer 18 may further comprise, in
addition to the conducting polymer, a dopant compatible with the
conducting polymer. The dopant may take the form of a polymeric dopant or
non-polymeric dopant. In the case of polymeric dopants, a matrix is formed
by the conducting polymer and dopant. Preferred polymeric dopants include
poly(styrene sulfonate) (as an acid or metal salt), poly(vinyl sulfate)
(as an acid or metal salt), poly(vinyl sulfonate) (as an acid or metal
salt), poly(anethosulfonate) (as an acid or metal salt) and poly(vinyl
stearate). Preferred non-polymeric dopants include p-toluene sulfonate,
trifluoromethane sulfonate and
{3-hydroxy-4[2-sulfo-4-(4-sulfophenylazo)phyenylazo]2,7-naphthalenesulfoni
c acid} and its metal salts. The electrochromic conducting polymer layer 18
may also contain combinations of two or more of the aforementioned
dopants.
Preferred conducting polymer/dopant combinations comprise combinations of
any of the conducting polymers listed in Table 1 with any of the dopants
listed in Table 2.
TABLE 1
______________________________________
Conducting Polymers
______________________________________
poly(diphenyl amine)
poly(4-amino biphenyl)
poly(aniline)
poly(3-alkyl thiophene) (alkyl = methyl through octyl)
poly(diphenyl benzidine)
______________________________________
TABLE 2
______________________________________
Dopants
______________________________________
poly(anethosulfonate)
poly(vinyl sulfate)
p-toluene sulfonate
trifluoromethane sulfonate
poly(vinyl stearate)
______________________________________
These combinations yield large dynamic range in the mid and far infrared
region, good visible region electrochromism, rapid switching speed, and
extended cyclability. In addition, these conducting polymer/dopant
combinations are thermally durable and possess good mechanical properties
including high film integrity. The conducting polymer/dopant combinations
do not crack or peel on repeated flexing.
When a conducting polymer is oxidized or reduced, the color of the
conducting polymer changes in the visible and infrared regions. During or
immediately subsequent to the redox process of the conducting polymer,
counterions may flow into or out of the conducting polymer to maintain
charge neutrality. For large ions, such as ClO.sub.4.sup.-, the counterion
flow induces recurrent morphological changes in the conducting polymer.
These morphological changes cause physical wear and tear and eventual
degradation of the conducting polymer.
In contrast, polymeric dopants do not physically move in and out of the
conducting polymer/dopant matrix. The polymeric dopant is enmeshed in the
conducting polymer. During oxidation and reduction of the conducting
polymer, counter-counterions move in and out of the conducting
polymer/dopant matrix. For example, in the case of the polymeric dopant
poly(vinyl sulfate), the counter-counterions are alkali metal or
H.sub.3.sup.+ O cations. These counter-counterions are significantly
smaller than the counterions in a conducting polymer with a non-polymeric
dopant. Since the counter-counterions are smaller than the counterions in
a conducting polymer with a non-polymeric dopant, fewer morphological
changes occur in the conducting polymer. Hence, there is less physical
wear and tear of a conducting polymer in a conducting polymer/polymeric
dopant matrix than in a conduct polymer with a non-polymeric dopant.
Compared to non-polymeric dopants, polymeric dopants allow for more rapid
switching, greater electrochromic efficiency and slower degradation of the
conducting polymer. Furthermore, polymeric dopants increase the
flexibility and mechanical durability of the conducting polymer.
The polymeric dopant utilized in the device of the present invention may
also contribute to the modulation of light in the infrared region. In some
cases, upon oxidation and reduction, morphological changes are induced in
the polymeric (or other macrocyclic) dopant. These morphological changes
are of the dimension of infrared light, especially long wave infrared
light. Thus, the dopants may alter the wavelength and intensity of light
in the infrared region. In particular, the dopants poly(anethosulfonate)
and poly(vinyl sulfate) can greatly modulate light in the infrared region.
Where a conducting polymer/dopant matrix is selected as the material
forming the electrochromic conducting polymer layer 18 and counter
electrode film 26, the conducting polymer/dopant matrix may be formed on
the substrate layers 20 and 28 of the electrodes by electrochemical
polymerization. The electrochemical polymerization is performed by placing
an electrode in a solution comprising a solvent containing the monomer and
dopant matrix. For aqueous-system electrochemical polymerization the
solvent is water; for nonaqueous-system electrochemical polymerization the
solvent is a nonaqueous solvent, e.g., an organic solvent such as
acetonitrite. A potential is applied across the electrode for a short
period of time, usually 1-10 minutes for aqueous polymerization systems,
and 5-45 minutes for nonaqueous polymerization systems. The result is the
formation of a conducting polymer/dopant matrix on the electrode.
The electrolyte in the electrochromic device 10 of the present invention
may comprise any liquid or solid electrolyte compatible with the
conducting polymer or conducting polymer/dopant combination in the
electrochromic conducting polymer layer 18. When the electrochromic
conducting polymer layer 18 contains a conducting polymer/dopant matrix,
the electrolyte should contain the polymeric dopant incorporated in the
conducting polymer/dopant matrix. The dopant in the electrolyte allows for
easier flow of ions between the electrolyte and conducting polymer/dopant
matrix.
For the conducting polymer poly(aniline) or a derivative thereof, an
aqueous liquid electrolyte is preferred. For example, a preferred liquid
electrolyte for a device containing the conducting polymer poly(aniline)
and a dopant in the electrochromic conducting polymer layer 18 comprises
deionized water, sulfuric acid and dopant.
A preferred liquid electrolyte for an electrochromic device, having the
conducting polymer/dopant matrix poly(aniline)/poly(vinyl
sulfate)-poly(anethosulfate), comprises a solution of 0.05 to 0.4 M
sulfuric acid, 0.02 to 0.4 M poly(vinyl sulfate) as a sodium or potassium
salt, and 0.002 to 0.025 M poly(anethosulfonate) in deionized water. The
solution may be heated for better dissolution of the ingredients.
Where a conducting polymer other than poly(aniline) is utilized for
electrochromic conducting polymer layer 18, a nonaqueous liquid
electrolyte is preferred over an aqueous liquid electrolyte.
A preferred liquid electrolyte for an electrochromic device, having the
conducting polymer/dopant combination poly(diphenyl amine)/p-toluene
sulfonate, comprises p-toluene sulfonate in acetonitrile or propylene
carbonate. Preferably, this liquid electrolyte for such a device comprises
0.02 to 0.4 M p-toluene sulfonate in acetonitrile.
For electrochromic devices containing acidic liquid electrolytes, such as
hydrochloric acid and sulfuric acid, the electrolyte may also contain one
or more gelling agents such as poly(vinyl alcohol) or poly(vinyl
pyrrolidone).
In order for gelled liquid electrolytes to achieve ambient temperature
conductivity adequate for acceptable electrochromic performance, the
electrolyte should maintain sufficient flow and liquid properties.
Electrolytes which meet this requirement typically take the form of highly
viscous gels.
The electrolyte in the electrochromic device 10 may take the form of a
solid electrolyte. The solid electrolyte may be prepared from an aqueous
or nonaqueous solution, that is, a solution comprising an aqueous solvent
(i.e., water) or a nonaqueous solvent (i.e., an organic solvent). A solid
electrolyte prepared from an aqueous solution is hereinafter referred to
as an "aqueous prepared solid electrolyte". A solid electrolyte prepared
from a nonaqueous solution is hereinafter referred to as an "nonaqueous
prepared solid electrolyte". In either case, the finished solid
electrolyte may or may not contain residual solvent from the preparation
process, but typically does so. The solid electrolyte will typically
contain about 5-10% residual solvent.
In an electrochromic device containing a conducting polymer/dopant matrix
including a polymeric dopant, a useful aqueous prepared solid electrolyte
may comprise an acidic electrolyte based on poly(vinyl alcohol)
incorporating the polymeric dopant. The poly(vinyl alcohol) allows the
electrolyte to form a solid. In such a solid electrolyte, the polymeric
dopant provides ion channels for the counter-counterions associated with
the polymeric dopant of the conducting polymer/dopant matrix. The ion
channels funnel the counter-counterions along the backbone of the
polymeric dopant of the electrolyte. This greatly increases the
conductivity of the electrolyte. Also, the polymeric dopant incorporated
in the electrolyte immobilizes the poly(vinyl alcohol). The polymeric
dopant of the electrolyte imparts much greater flexibility, mechanical
durability and integrity than the poly(vinyl alcohol) electrolyte would
possess without the polymeric dopant. The solid electrolyte and the
conducting polymer/dopant matrix contain the same dopant. Thus, the solid
electrolyte is compatible with the conducting polymer/dopant matrix.
A preferred solid electrolyte composition comprises sulfuric acid,
poly(anethosulfonate), poly(vinyl sulfate), poly(vinyl alcohol), and water
in the following molar proportions: 100-800 sulfuric acid; 1-200
poly(anethosulfonic acid); 20-800 poly(vinyl sulfate); 2000-10000
poly(vinyl alcohol); and water (molar proportions of polymers are based
upon monomer). The solid electrolyte may be prepared, for example, by
mixing a solution of 0.0005 to 0.1 M poly(anethosulfonate), 0.01 to 0.4 M
poly(vinyl sulfate), 0.05 to 0.4 M sulfuric acid, and 1 to 5 M poly(vinyl
alcohol) in 15 to 50 mL (0.83 to 2.8 moles) deionized water. The average
molecular weight of the poly(vinyl alcohol) may vary substantially, but is
typically about 200,000. The solution is then heated with stirring to a
temperature between about 60.degree. C. and the boiling point of the
solution, until the ingredients are dissolved. From about 0.05 to about 1
w/w % poly(ethylene-co-methyl acrylate-co-acrylic acid) may optionally be
added to the solution to further improve the mechanical properties of the
electrolyte. The volume of the solution is then reduced by 5 to 70% by
evaporation. From about 1% to about 85% of the original amount of
deionized water remains in the electrolyte after evaporation. The solution
is solidified by cooling with stirring to yield the solid electrolyte.
A preferred nonaqueous solid electrolyte for use in the electrochromic
device of the present invention is comprised of poly(ethylene oxide),
poly(ethylene glycol), a dopant identical to the dopant in the conducting
polymer/dopant matrix and a polymer additive to enhance ion conduction.
The polymer additive may comprise, for example, a mixture of poly(vinyl
sulfate) and one or more of poly(anethosulfonate), poly(ethyl or methyl
methacrylate), or poly(ethylene-co-methyl acrylate-co-glycidyl
methacrylate) (PEMAGM).
One preferred nonaqueous prepared solid electrolyte comprises 0.1 to 1 w/w
% of PEMAGM, 0.2 to 4 w/w% poly(ethyl or methyl methacrylate), and the
following additional components in the following molar proportions:
50-1000 poly(ethylene oxide); 10-100 poly(ethylene glycol); 1-50 p-toluene
sulfonate; 10-50 trifluoromethane sulfonate; 1-5 poly(vinyl sulfate); 1-5
poly(anethosulfonate); and acetonitrile.
To form the aforementioned solid electrolyte, a solution is first prepared
containing 0.05 to 1.0 M of poly(ethylene oxide), 0.01 to 0.1 M of
poly(ethylene glycol) 0.001 to 0.05 M of p-toluene sulfonate, 0.01 to 0.05
M trifluoromethane sulfonate, 0.001 to 0.005 M of poly(vinyl sulfate)
and/or poly(anethosulfonate), 0.2 to 4 w/w % of poly(ethyl or methyl
methacrylate), 0.1 to 1 w/w % of PEMAGM and 40 to 150 mL acetonitrile. The
average molecular weight of the poly(ethylene oxide) may vary
substantially, but is typically about 600,000 g/mol. The average molecular
weight of the poly(ethylene glycol) may vary substantially, but is
typically about 1,500 g/mol. The solution is heated with stirring until
the contents of the solution are dissolved. The acetonitrile is then
slowly evaporated off in a rotary evaporator or on a vacuum line, yielding
the solid electrolyte. Approximately, between 1% and 85% of the original
amount of acetonitrile remains in the electrolyte.
Once the working electrode formed by electrochromic conducting polymer
layer 18 and electrolyte-permeable substrate layer 20, and the counter
electrode formed by counter electrode film 26 and second substrate layer
28, are fabricated and the electrolyte is synthesized, a coating is
directly applied to the exposed conducting polymer layer outer surface 15
to create a transparent outer layer 12. The coating also serves to protect
the device from minor abrasive effects and damage.
The coating forming transparent outer layer 12 may comprise any flexible
material which is substantially (at least approximately 50% transmission)
transparent in the visible region of the electromagnetic spectrum. The
coating should also be substantially transparent in the infrared region
when applied to the working electrode as a thin coating. Preferred coating
materials include poly(ethylene terephthalate) and other polyesters,
poly(ethylene), poly(propylene), poly(methyl methacrylate), poly(ethyl
methacrylate), acrylics (such as methyl methacrylate synthetic resins,
acrylate synthetic resins, and thermoplastic poly(methyl
methacrylate)-type polymers), acrylonitrile methyl acrylate copolymers,
ethylene vinyl acetate, fluorinated ethylenepropylene resins, fluorinated
poly(alkylenes), polyvinyl alcohol and poly(ethylene glycol), poly(vinyl
chloride), and any combination thereof. More preferred coating materials
are poly(ethyl methacrylate), poly(ethylene), acrylics, and poly(ethylene
terephthalate). Most preferably, the coating is poly(ethylene).
Preferably, the coating is applied by heat sealing or coated onto the
conducting polymer surface 15. Where the coating is composed of poly(ethyl
methacrylate), the coating material is preferably applied in the form of a
solution in an organic solvent, such as acetonitrile or toluene.
The temperature of the heat applied and the duration that the heat is
applied are critical when heat sealing the coating to the conducting
polymer surface 15. If the sealing is not performed properly, the
conducting polymer may become moribund or damaged. More importantly, the
electrolyte may be unable to contact the conducting polymer surface 15 if
the heat sealing is not properly performed.
The coating poly(ethylene) is preferably heat sealed to the conducting
polymer surface 15. The poly(ethylene) is preferably in the form of a thin
sheet, having a preferable thickness from about 0.25 to about 1.5 mil (6
to 38 .mu.m). The thin sheet may be heat sealed directly onto the
conducting polymer surface 15 of the working electrode. During the heat
sealing of the coating to the conducting polymer surface 15, the
temperature of the heat applied and the duration that the heat is applied
need to be controlled to avoid damage and degradation to the
electrochromic conducting polymer layer 18.
For a device comprising the coating poly(ethylene) and the preferred
conducting polymer/dopant combinations of the present invention, a heat
seal temperature between 90.degree. C. and 140.degree. C. for 1 to 30
seconds is preferred. The temperature and duration may vary depending on
the thickness of the poly(ethylene) and the specific conducting
polymer/dopant combination.
A preferred coating composition for application of poly(ethyl methacrylate)
as the coating to the conducting polymer surface 15 comprises 1 to 5 w/w %
poly(ethyl methacrylate) in acetonitrile or toluene. The coating is
preferably applied to the dry conducting polymer surface 15 on the working
electrode with an applicator. The coating should completely cover the
conducting polymer surface 15 while being as thin as possible.
The coating applied to conducting polymer surface 15 to form transparent
outer layer 12 may be extended to encase the entire electrochromic device,
except for a small fill hole on the top of the device located between the
working electrode and the counter electrode, to form the encapsulant 34.
Alternatively, the encapsulant 34 may be comprised of a different coating
than the transparent outer layer 12. The coating is applied to the back
and sides of the device. The coating does not have to extend around all
the exposed surfaces of the electrodes. The electrical connectors 36 and
38 should remain exposed. The encapsulant 34 serves to protect the device
from minor abrasive effects and damage.
The liquid or molten solid electrolyte may be poured into the device, after
the coating is applied, through the small fill hole. During pouring, the
device may be manipulated to allow the electrolyte to uniformly form
between the working electrode and the counter electrode. Once the
electrolyte is poured into the device, the fill hole is sealed. The fill
hole may be sealed immediately or several days after filling.
To install a solid electrolyte into the electrochromic device of the
invention, the solid electrolyte may be reheated until it melts. The
melted electrolyte may then be poured into the electrochromic device. The
electrolyte solidifies when the electrochromic device is cooled. Further
solvent loss from the electrolyte occurs after the electrolyte is poured
onto the device and before sealing of the fill hole.
When a melted solid electrolyte is poured into the electrochromic device,
capillary action in the device forces the solid electrolyte into the pores
of the electrolyte-permeable substrate layer 20. This creates edge-effect
electrolytic contact between the electrochromic conducting polymer layer
18 and the solid electrolyte. The electrolyte-permeable substrate layer 20
may be massaged through the transparent outer layer 12 and encapsulant 34
or soaked in solid electrolyte to ensure a good distribution of the solid
electrolyte in the pores of the substrate layer 20.
As shown in FIG. 3A, after the electrochromic device 10 is assembled, the
electrolyte 70 is contained in the pores of the first porous substrate
layer and contacts the electrochromic conducting polymer layer 18. The
electrical contact between the electrolyte 70 and the electrochromic
conducting polymer layer 18 is an edge effect rather than a surface
effect. Therefore, there is minimal direct contact between the conducting
polymer surface 15 and the electrolyte 70.
In order to increase the electrical contact between the electrolyte and the
electrochromic conducting polymer layer, the device should be "broken-in"
by cycling the device up to 100 times between its extreme electrochromic
states before being put to use. Cycling is performed by varying the
applied potential across the device to yield different electrochromic
states.
FIG. 3B shows the electrochromic device 10 after assembly and "break-in".
Break-in leads to the formation of ion channels 72 in the electrochromic
conducting polymer layer 18. After break-in, the edge contact between the
electrolyte 70 and the electrochromic conducting polymer layer 18 is
sufficient to permit adequate conduction through the electrochromic
conducting polymer layer 18 due to the ion channels 72.
The electrochromic conducting polymer swells during the "break-in" process.
The polymer swells and contracts during doping and de-doping, i.e.
oxidation and reduction, of the polymer, but to a lesser extent. Oxidation
or reduction of the electrochromic conducting polymer occurs when the
potential applied across the electrochromic device is varied. A rigid
encapsulant, such as glass, would impede the swelling and contracting of
the polymer. Therefore. a flexible encapsulant is required to permit the
swelling and contracting of the electrochromic conducting polymer.
An electrochromic conducting polymer may be a p-type or n-type conducting
polymer. P-type conducting polymers in their reduced state are
substantially transparent. P-type conducting polymers in their oxidized
state, are highly absorptive.
In operation, the color of the electrochromic conducting polymer layer 18
may be changed by varying the potential applied across the electrochromic
conducting polymer layer 18. In one embodiment of the device, the
electrochromic conducting polymer layer 18 comprises a p-type conducting
polymer. To change the color of the electrochromic device, the potential
across the conducting polymer is varied. When a positive potential is
applied to the electrochromic conducting polymer layer 18, the conducting
polymer becomes highly colored, i.e., has high absorption. As the
potential applied to layer 18 is decreased and becomes negative, the
conducting polymer becomes more transparent and less absorptive. When the
electrochromic conducting polymer reaches its fully reduced state, it is
substantially transparent.
The intensity of incident visible as well as infrared light reflected by
the device may be altered by the conducting polymer/dopant matrix. The
dopant may contribute substantially to the absorption and scattering of
the incident light. The scattering of the incident light is also dependent
on the particle size and conductivity of the conducting polymer/dopant
matrix. Both the particle size and conductivity of the conducting
polymer/dopant matrix vary with the amount of applied potential.
Therefore, the intensity of incident light reflected by the electrochromic
device may be varied by altering the potential applied to the conducting
polymer/dopant matrix.
Devices according to the present invention containing a
poly(aniline)-poly(vinyl sulfate)/poly(anethosulfonate) conducting
polymer/dopant matrix provide color in the visible spectral region ranging
from glass-clear-transparent upon application of a negative potential
through light green, dark green, green-blue and a very dark
green-blue-black as the potential is increased. Glass clear transparency
under negative potential is also exhibited, for instance, by the
conducting polymers poly(diphenyl amine) and poly(diphenyl benzidine) when
combined with an appropriate dopant. In the IR spectral region, when a
positive potential is applied, the device exhibits a broad band low
reflectance at wavelengths from about 2.5 to about 23 .mu.m. At negative
applied potentials, the device exhibits broad band high reflectance.
The reflectance of poly(aniline)-poly(vinyl sulfate)/poly(anethosulfonate)
devices steadily increases as the applied potential decreases. The
reflectance of the device is slightly masked when the conducting polymer
surface 15 is coated with a poly(ethylene) coating. The poly(ethylene)
coating absorbs light at wavelengths of about 7, 9 and 13 .mu.m. The
reflectance of the device is undistorted when a thin coating, such as
poly(ethyl methacrylate), instead of poly(ethylene) is applied to the
conducting polymer surface 15. The reflectance of the device is virtually
unaffected by a poly(ethylene) coating in the near-infrared region 0.8 to
1.2 .mu.m, mid-infrared region 3 to 5 .mu.m and long wave infrared region
8 to 14 .mu.m. The dynamic range of the device is large in the visible and
infrared regions.
Devices according to the present invention containing poly(aniline) in the
electrochromic conducting polymer layer 18 have switching times from
extreme dark to light states of from about 0.1 to about 1.0 seconds
(transition from 10% to 90% of steady state).
Devices according to the present invention containing the conducting
polymer/dopant combination poly(diphenyl amine)/p-toluene sulfonate
provide color ranging from transparent upon application of a negative
potential through light green, to dark green, to dark green-brown upon
application of a positive potential. In the near-infrared region 0.8 to
1.2 .mu.m, mid-infrared region 3 to 5 .mu.m and long wave infrared region
8 to 14 .mu.m, the conducting polymer/dopant combination poly(diphenyl
amine)/p-toluene sulfonate exhibits large and broad band dynamic range
similar to poly(aniline) devices. The switching time between extreme
electrochromic states in poly(diphenyl amine)/p-toluene sulfonate devices
is from about 0.5 to about 1.5 sec (10%-90% steady state).
A DC potential may be continuously applied to the electrochromic material
until the desired electrochromic state is achieved. The DC potential may
then be removed, if the electrochromic material has good open circuit
memory. In order to maintain the electrochromic material at the
electrochromic state, the electrochromic material should be periodically
refreshed. The electrochromic material may be refreshed by the application
of a DC potential to the electrochromic material, identical to the initial
DC potential. The potential may be pulsed or continuously applied to the
electrochromic material.
The continuous application of a DC potential to maintain a desired
electrochromic state causes the electrochromic material to constantly
experience an electrochemical current. This causes physical wear and tear
of the electrochromic material resulting in degradation of the
electrochromic material.
A pulse method of control may be applied to the device to achieve the
desired electrochromic state. Such a pulsed method may cause minimal
physical wear and tear of the electrochromic material. This would
significantly increase the cyclability of the device.
One pulse method is to apply a potential significantly greater than the
desired potential to the device for short periods of time. For example, if
the desired electrochromic state requires a potential (equilibrium or open
circuit) of +0.7 V, a potential of between +1.0 and +3.0 V may be pulsed
for a duration of milliseconds or microseconds. The pulses are spaced with
comparatively long rest periods, e.g., 100 milliseconds rest periods. With
each successive pulse, the open circuit or equilibrium potential of the
electrochromic material approaches the desired +0.7 V. A sensing circuit
measures the open circuit potential of the device. As the potential across
the electrochromic material approaches the desired +0.7 V, the magnitude
of the pulse is reduced. For example, if the original voltage was +2.0 V,
it may be reduced to +0.5 V as the electrochromic material nears +0.7 V.
The control circuit may be assembled with commercial off-the-shelf
electronic components and custom written software. Preferably, a personal
computer controls the potential applied to the device. This control method
increases cyclability of electrochromic devices by an average of one to
two orders in magnitude.
The device of the present invention, comprising an outer flexible layer in
intimate contact with an underlying electrochromic conducting polymer
layer, embodies a significant departure from prior electrochromic devices
in which these layers were spaced apart and separated by electrolyte.
Surprisingly, the devices of the present invention are clectrochromically
active even though access of electrolyte and ions to the surface of
electrochromic conducting polymer 18 is blocked by that layer's intimate
contact with outer layer 12.
Accessibility of the electrolyte, and thus electrical contact with the
electrochromic conducting polymer layer 18, is from the side in the
present devices. Thus, electrolyte contact is an edge effect rather than a
surface effect, (FIG. 3A). Since there is no direct electrical contact of
the electrochromic conducting polymer surface via electrolyte, the devices
of the invention must be cycled repeatedly between extreme electrochromic
states to attain substantial void space and swelling of the electrochromic
conducting polymer, which results in formation of conduction and ion
channels as in FIG. 3B.
Because outer layer 12 and electrochromic conducting polymer layer 18 are
in intimate contact, electrolyte will not accumulate between them. Thus,
unlike prior electrochromic devices, there is no intervening electrolyte
to absorb incident light before being modulated by the electrochromic
conducting polymer. This is a substantial improvement over prior devices
in which incident light must pass through a region of electrolyte before
reaching the electrochromic material layer. Although the electrolytes
which have been used in prior devices may have been substantially
transparent in the visible region of the electromagnetic spectrum, they
have been typically highly absorbing in the infrared region. Thus, even
very thin layers of electrolyte were responsible for significant infrared
signal reduction.
The devices of the present invention, which dispense with electrolyte
between the outer layer 12 and the electrochromic material, do not suffer
from the aforesaid infrared signal reduction due to absorption by
electrolyte. Moreover, since the incoming light is not forced to pass
through the electrolyte, opaque or even infrared-opaque solid or liquid
materials may be employed as electrolytes, since they will not interfere
with the working electrode's signal modulation.
EXAMPLES
In the Examples which follow, electrochemical polymerization of each
conducting polymer onto each electrode was performed in 3-electrode mode
(Pt quasi reference electrode) with a Princeton Applied Research Corp.
(PARC) Model 263 potentiostat/galvanostat controlled by a personal
computer running PARC's 250/270 software. In some experiments a
Bioanalytical Systems Model PWR-3 high current potentiostat was used in
lieu of the PARC Model 263 potentiostat.
Diffuseultraviolet-visible-nearinfrared (UV-Visible-NIR), diffuse infrared
(diffuse IR), specular UV-Visible-NIR, and specular infrared (specular IR)
spectroscopy was performed on each device while maintaining a constant
potential across the electrochromic material of the device. The potential
to apply across each device was determined from the characterization
cyclic voltammogram of the device. The cyclic voltammogram varied slightly
between devices, even devices having identical conducting polymer/dopant
combinations. Thus, the potential applied to each device varied.
Infrared spectroscopy was performed with a Perkin-Elmer Model 1615 Fourier
Transform Infrared (FTIR) spectrometer controlled by a personal computer
running Perkin-Elmer's Grams-Analyst software. Specular and diffuse
reflectance were measured with reflectance measurement adapters
manufactured by LabSphere for Perkin-Elmer. The specular IR measurements
were referenced to a mirror supplied by Perkin-Elmer. The diffuse IR
measurements were referenced to FTIR-grade KBr powder (Aldrich Chemical)
as instructed by Perkin-Elmer. In the case of the diffuse IR measurements,
reflected energy was maximized prior to each run. The reference KBr powder
was a much poorer scatterer than the electrochromic devices tested. This
caused reflectance values greater than 100% to be frequently obtained.
UV-Visible-NIR reflectance measurements were performed with a Perkin-Elmer
Model Lambda-12 spectrophotometer controlled by a personal computer
running Perkin-Elmer's UVWinlab software. Specular and diffuse
UV-Visible-NIR reflectance were measured with reflectance measurement
adapters manufactured by LabSphere for Perkin-Elmer. The specular
UV-Visible-NIR measurements were referenced to a mirror. The diffuse
UV-Visible-NIR measurements were referenced to a Spectrolon (BaSO.sub.4)
sphere supplied by Perkin-Elmer.
Example 1
The substrate of the working electrode was a microporous poly(vinylidene
fluoride) membrane, which was commercially obtained. The substrate of the
counter electrode was a thin, non-porous poly(ethylene terephthalate)
sheet. Gold was deposited onto the substrates of both electrodes to a
thickness of 300 nm by DC magnetron sputtering. The substrates were then
cut with scissors to 2.5 cm.times.5 cm (1".times.2"). The counter
electrode was cut in such a fashion that a small strip protruded from the
counter electrode. The small strip permitted easy electrical connection to
an electrical source.
Electrochemical polymerization of poly(aniline) was performed on each
electrode to form a poly(aniline) film on each electrode. Each electrode
was placed in a deionized water solution containing 0.2 M H.sub.2
SO.sub.4, 0.2 M K salt of poly(vinyl sulfate), 0.005 M salt of
poly(anethosulfonate) and 0.05 M aniline.
A potential of +0.8 V (vs. Pt quasi reference) was applied for 1 minute to
the working electrode while in the deionized water solution. After the 1
minute, a potential of +0.6 V was applied for 2 minutes to the working
electrode.
A potential of +0.8 V (vs. Pt quasi reference) was applied for 1 minute to
the counter electrode while in the deionized water solution. After the 1
minute, a potential of +0.6 V was applied for 3 minutes to the counter
electrode.
The electrodes were washed in deionized water and dried.
A liquid electrolyte was prepared by mixing a solution of 0.2 M H.sub.2
SO.sub.4, 0.004 M poly(anethosulfonate), and 0.2 M K salt of poly(vinyl
sulfate) in deionized water. The solution was heated to 60.degree. C. with
stirring. The solution was evaporated to 90% of its original volume. The
solution was then cooled.
Poly(ethylene) having a thickness of 1.15 mil (29 .mu.m) was heat sealed
onto the exposed conducting polymer surface of the working electrode at
about 103.degree. C. for 5 seconds. The working electrode and the counter
electrode were positioned such that the gold surface of the counter
electrode faced the non-metallized surface of the substrate of the working
electrode. A small gap separated the working electrode and the counter
electrode. Poly(ethylene) having a thickness of 1.15 mil was heat sealed
around the electrodes at about 103.degree. C. for 5 seconds. The
previously heat sealed conducting polymer surface was not heat sealed with
the poly(ethylene) having a thickness of 1.15 mil. A small fill hole
between the two electrodes was formed by the poly(ethylene). An electrical
connector tab was heat sealed onto the gold surface of the substrate of
the working electrode.
The liquid electrolyte was poured into the fill hole. The device was gently
massaged to uniformly spread the electrolyte. Excess electrolyte was
squeezed out of the device through the fill hole. The fill hole was then
heat sealed.
The device was repeatedly cycled between +0.5 V and -0.5 V (2-electrode
mode) until a recognizable cyclic voltammogram was observed. The potential
limits were then extended until two peaks were observed in the
voltammogram. Typically, the cycling limits were extended to +0.8 V and
-0.8 V, although the cycling limits varied from device to device.
The end point potentials of the voltammogram and three potentials
approximately equi-distant between the end point potentials were selected
from the cyclic voltammogram. The diffuse UV-Visible-NIR, diffuse IR,
specular UV-Visible-NIR and specular IR spectra were obtained for the
device at each of these applied potentials.
FIGS. 4, 5 and 6 are specular FTIR, diffuse FTIR, and diffuse UV-Vis-NIR
spectra, respectively, for this device. The specular UV-Visible-NIR
spectra (not shown) did not convey any information beyond the information
conveyed by diffuse UV-Visible-NIR spectras. The spectra were obtained
while maintaining a constant potential (2-electrode mode) across the
device. As illustrated in FIGS. 4, 5 and 6, the dynamic range of the
device was very substantial.
The absorptions at the wavelengths 7, 9 and 13 .mu.m, which mask the
dynamic range near those wavelengths, are characteristic of
poly(ethylene), which forms the encapsulant. The application of a thinner
poly(ethylene) layer on the surface of the working electrode would reduce
this masking substantially.
In the diffuse UV-Visible-NIR spectra, the dynamic range was less broad
band then in the spectra FTIR and diffuse FTIR spectras. A broad
reflectance maximum at 620 nm, indicative of the transparent to green to
dark green-blue-black color change of this device.
Example 2
The device was substantially identical to the device in Example 1, except
that the substrate of the working electrode was a microperforated
poly(ethylene terephthalate) membrane instead of a microporous
poly(vinylidene fluoride) membrane.
FIGS. 7, 8 and 9 are specular FTIR, diffuse FTIR and diffuse UV-Vis-NIR
spectra, respectively, of the device. The observed dynamic range of the
device in the infrared region was very substantial. The color changes of
the device in Example 2 in the visible region were identical to the color
changes exhibited by the device in Example 1.
Example 3
The device was substantially identical to the device in Example 1, except
that a thin coating of poly(ethyl methacrylate) was applied to the exposed
conducting polymer surface of the working electrode in lieu of
poly(ethylene). The substrate of the working electrode was composed of
nylon in lieu of poly(vinylidene fluoride). The encapsulant coating
solution was a 5 w/w % solution of poly(ethyl methacrylate) in toluene.
The encapsulant coating solution was prepared by heating the ingredients
with stirring until the poly(ethyl methacrylate) dissolved and filtering
the resulting solution. The coating was applied manually with an
applicator to form an even, thin film surrounding the device.
FIGS. 10, 11 and 12 are specular FTIR, diffuse FTIR and diffuse UV-Vis-NIR
spectra, respectively, of the device. Unlike the devices in Examples 1 and
2, the dynamic range of the device in Example 3 is not masked at the
wavelengths 7, 9 and 13 .mu.m in the infrared region, since the
encapsulant is composed of poly(ethyl methacrylate) instead of
poly(ethylene). The dynamic range in the visible and infrared regions of
the device in Example 3 is also substantially larger than the dynamic
ranges of the devices in Examples 1 and 2.
Example 4
The device was substantially identical to the device in Example 2, except
that the electropolymerization solution comprised 0.2 M H.sub.2 SO.sub.4
and 0.2 M salt of poly(anethosulfonate) in deionized water. The
electrolyte solution before heating comprised 0.02 M H.sub.2 SO.sub.4 and
0.2 M poly(anethosulfonate) in deionized water.
FIG. 13 is the characterization cyclic voltammogram for this device. Two
peaks are observed in the characterization cyclic voltammogram. These
peaks are characteristic of most poly(aromatic amines). In FIGS. 14, and
16, specular FTIR, diffuse FTIR and specular UV-Visible-NIR spectra,
respectively, of the device are shown.
Examples 5-8 are comparative examples illustrating the significant and
dramatic improvements of the present invention over the prior art.
Comparative Example 5
The device in Example 5 was substantially identical to the device in
Example 2, except that, as in U.S. Pat. No. 5,446,577, issued to Bennett
et al., a layer of electrolyte was inserted between the conducting polymer
surface of the working electrode and the encapsulant.
FIGS. 17 and 18 are specular FTIR and diffuse FTIR spectra, respectively,
of the device. Comparison of FIGS. 17 and 18 with FIGS. 7 and 8 of the
device in Example 2 illustrates the dramatic decrease in dynamic range in
the infrared region when a layer of electrolyte is inserted between the
working electrode and the encapsulant, especially in the regions 3 to 5
.mu.m and 8 to 14 .mu.m.
Comparative Example 6
The device was substantially identical to the device in Example 2, except
that the conducting polymer/dopant combination in the device in was
Poly(pyrrole)/ClO.sub.4. The electropolymerization solution comprised 0.05
M pyrrole monomer, 0.2 M ClO.sub.4, and acetonitrile. The electrochemical
polymerization of the electrodes was performed with the potentials of +0.6
V and +0.5 V (double step, vs. Pt quasi-reference) instead of +0.8 V and
+0.6 V. The thickness of the conducting polymer/dopant film was selected
to correspond to that of the poly(aniline) film in Example 2. Variations
in the thickness of the conducting polymer/dopant film were tested and had
negligible effect on the dynamic range of the device. Each electrode was
washed in acetonitrile and dried before the device was assembled.
FIGS. 19 and 20 are specular FTIR and diffuse FTIR spectra of the device.
As shown in FIGS. 19 and 20, the dynamic range of the device is
negligible. The conducting polymer/dopant combination of this device is
almost non-responsive in the infrared region.
Comparative Example 7
The device was substantially identical to the device in Example 6, except
that p-toluene sulfonate was used in lieu of ClO.sub.4. The conducting
polymer electropolymerization was performed at +1.2 V and 1.1 V (vs. Pt
quasi reference) instead of +0.8 V and +0.6 V.
FIG. 21 is a specular FTIR spectrum of the device. The device exhibited
negligible dynamic range in the infrared region. Varying the dopant in the
device negligibly effected the dynamic range of the device in the infrared
region. Hence, the conducting polymer was nonresponsive in the infrared
region.
Comparative Example 8
The device was substantially identical to the device in Example 2, except
that the electropolymerization solution comprised 0.2 M H.sub.2 SO.sub.4.
FIGS. 22, 23 and 24 are specular FTIR, diffuse FTIR and diffuse
UV-Visible-NIR spectras, respectively, of the device. The device exhibited
poor dynamic range.
Comparative Example 9
The device in Comparative Example 9 was substantially identical to the
device in Example 2, except that the electropolymerization solution
comprised poly(styrene sulfonate) as a Na salt. The conducting
polymer/dopant combination was poly(aniline)/poly(styrene sulfonate),
which was identical to that used in U.S. Pat. No. 5,253,100, issued to
Yang et al.
FIGS. 25, 26 and 27 are specular FTIR, diffuse FTIR and specular
UV-Visible-NIR spectra, respectively, of the device. The device did not
contain any of the aforementioned preferred dopants. The infrared response
of the device was very poor, as shown by FIGS. 25, 26 and 27. Hence, the
dopant is critical to the infrared response of the device.
FIG. 28 is a bar graph comparing the diffuse reflectance dynamic ranges at
5 .mu.m of the devices in Example 2 and Comparative Examples 5, 6, 8 and
9. FIG. 28 illustrates that both the device design and the conducting
polymer/dopant combination are critical determinants of the infrared
response and dynamic range of the electrochromic device.
Example 10
The device in Example 10 was substantially identical to the device in
Example 1, except that a solid electrolyte was used in lieu of the liquid
electrolyte.
The solid electrolyte was prepared by mixing a solution comprising 0.005 M
poly(anethosulfonate), 0.25 M poly(vinyl sulfate), 0.2 M H.sub.2 SO.sub.4,
and 4.36 M poly(vinyl alcohol) (Avg MWt 186,000) in 25 mL deionized water.
The solution was heated to just boiling until the contents of the solution
dissolved. The volume of the solution was reduced to 90% of its original
volume. Then, the solution was cooled. The solid electrolyte was reheated
until it became fluid. The heated solid electrolyte was poured into the
fill hole of the device. The fill hole was finally heat sealed after
letting the device rest unsealed for 3 days.
FIGS. 29 and 30 are specular FTIR and diffuse FTIR spectra, respectively,
of the device. The poly(ethylene) encapsulant absorptions at the
wavelengths 7, 9 and 13 .mu.m somewhat mask the otherwise very
substantial, broad band dynamic range of the device in FIGS. 29 and 30.
Example 11
The device in Example 11 was substantially identical to the device in
Example 2, except that the solid electrolyte described in Example 10 was
incorporated in the device in lieu of the liquid electrolyte in Example 2.
The electrochemical polymerization solution comprised 0.2 M H.sub.2
SO.sub.4, 0.4 M K salt of poly(vinyl sulfate), 0.005 M salt of
poly(anethosulfonate) and 0.05 M aniline.
FIGS. 31, 32 and 33 are specular FTIR, diffuse FTIR, and diffuse
UV-Visible-NIR spectras, respectively, of the device. As shown by FIGS.
31, 32 and 33, substantial tailoring of the infrared response of the
device can be achieved by altering the conditions during
electropolymerization. The dynamic ranges of the device in the infrared,
visible, and ultraviolet regions are especially large. The dynamic range
is especially large and broad band in the extreme long wave infrared
region 10 to 20 .mu.m. The poly(ethylene) encapsulant masks the dynamic
range of the device at 13 .mu.m.
Example 12
The device was substantially identical to the device in Example 2, except
that poly(3-methyl thiophene) doped with a fluorinated anionic dopant was
used in lieu of poly(aniline). The conducting polymer
electro-polymerization was performed at +1.05 V and +0.9 V (vs. Pt
quasi-reference) instead of +0.8 V and +0.6 V. The electropolymerization
solution was an acetonitrile solution of 0.05 M monomer and 0.2 M
fluorinated dopant. The electrodes were washed with acetonitrile before
use.
FIGS. 34, 35 and 36 are specular FTIR, diffuse FTIR, and diffuse
UV-Visible-NIR spectras, respectively, of the device. The device exhibited
broad band and large dynamic range in the infrared region as shown in
FIGS. 34, 35 and 36. The poly(ethylene) encapsulant partially masks the
dynamic range of the device in the infrared region. This device, however,
exhibits a smaller dynamic range in the visible region, as shown in FIG.
36, than the device in Example 2. The device in Example 12 does not
exhibit the glass clear transparency in the visible region, when the
conducting polymer is in the most reduced state which is characteristic of
poly(aromatic amines).
Example 13
The device in Example 13 was substantially identical to the device in
Example 2, except that the conducting polymer/dopant combination was
poly(diphenyl amine)/p-toluene sulfonate instead of poly(aniline). The
electropolymerization solution was an acetonitrile solution of 0.05 M
poly(diphenyl amine) monomer and 0.2 M p-toluene sulfonate dopant. The
electropolymerization was performed at the potentials +1.2 V (vs. Pt
quasi-reference) and +1.1 V instead of +0.8 V and +0.6 V. The electrodes
were washed with acetonitrile and dried prior to assembly of the device.
The electrolyte was a solid electrolyte instead of a liquid electrolyte.
The solid electrolyte was prepared by mixing a solution containing 0.76 M
of poly(ethylene oxide), 0.086 M of poly(ethylene glycol) (Avg MWt 1,500),
0.005 M of p-toluene sulfonate, 0.15 M trifluoromethane sulfonate, 0.003 M
of poly(vinyl sulfate), 0.003M of poly(anethosulfonate), and 1 w/w % of
the poly(ethyl methacrylate), and 75 mL (1.436 moles) acetonitrile. The
average molecular weight of the poly(ethylene oxide) was 600,000 g/mol.
The solution was heated with stirring until the ingredients of the
solution dissolved. The acetonitrile was then slowly evaporated off on a
vacuum line, yielding the solid electrolyte. The electrolyte was then
reheated until the electrolyte was molten. The electrolyte was then poured
into the fill hole of the device. The fill hole was heat sealed.
FIG. 37 is a specular FTIR spectrum of the device. The device exhibited
large dynamic range in the long wave infrared region beyond 10 .mu.M.
The present invention may be embodied in other specific forms without
departing from the spirit or essential attributes thereof and,
accordingly, reference should be made to the appended claims, rather than
to the foregoing specification, as indicating the scope of the invention.
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